Steel caterpillars have usually been attached to the under-carriages of traveling construction machines, but in recent years rubber crawlers have been applied as well.
FIG. 9 shows a conventional rubber crawler 16 on which an idler wheel 19 is rolling. The reference numeral 11 is a core bar. The reference numerals 12, 13 and 14 indicate a wing portion, a protruding part to prevent disengagements of a wheel, and an engaging part with a driving wheel, respectively, all of the core bar 11. The numeral 17 is a steel cord, 18 is an engaging hole, and 19c is a center rolling part of the idler wheel 19. As shown in this figure, the center rolling part 19c travels between protruding parts 13, 13 so that disengagements of the wheel can be prevented.
Compared with a steel crawler, the above rubber crawler has the disadvantage that disengagements of the crawler may easily happen. This is mainly because the rubber crawler is partially twisted to thereby disengage from the wheel, when it turns on a stepped ground in the workshop. FIG. 10 shows disengagement of the wheel. The crawler is slided sideways between the adjacent core bars 11, 11, and therefore the center rolling part 19c of the idler wheel 19 runs on the protruding part 13, thereby causing the disengagement 20 of the wheel from the crawler.
To overcome this problem, increasing the widthwise strength of the rubber crawler may be considered. Then, if the interval of core bars in the rubber crawler is narrowed as the width thereof is broadened in order to increase the strength of the rubber crawler, the widthwise edge portions of each core bar become angulate at their turning point, which places the rubber crawler in a polygonal shape. Accordingly, the rubber crawler suffers much bending fatigue, and therefore its durability decreases.
On the other hand, if a short-pitched rubber crawler (wherein the core bars' interval is half of the conventional rubber crawler's core bar interval by embedding core bars of narrower width arranged for the interval) is applied in order to increase the strength, it is excellent in preventing disengagements of a wheel because of the narrower interval of the embedded core bars than in a conventional rubber crawler, and is excellent in the durability as well. However, this has not become a perfect means yet, but still causes disengagements of the crawler in a large-sized construction machine.